In general, image signals received by most display devices are analog signals. An image is composed of different color signals (brightness gray-scale values) represented by different voltages. Referring to FIG. 2A, a color signal 1 includes a set of minimum brightness voltages 11 and a set of maximum brightness voltages 12. The color signal 1 causes liquid crystal molecules in a display device to twist and thus change the amount of light that can pass through a liquid crystal layer. The period of time during which the brightness rises from 10% to 90% is referred to as a rise time, and the period of time during which the brightness falls from 90% to 10% is referred to as a fall time.
When the color signal 1 is transmitted through a transmission cable, the impedance of the transmission cable may attenuate the signal, or interference in the transmission cable may distort the signal. The set of the minimum brightness voltages 11 and the set of the maximum brightness voltages 12 tend to have surge points caused by attenuation or interference. The presence of such surge points may cause the display device to misjudge the level of the image signal. For example, if the brightness gray-scale has a maximum value of 255, and a minimum value of 0, then attenuation or interference may cause the maximum value of an analog signal received by a display device to be equal to only 253 and not the maximum value of 255, while the minimum value of the analog signal may be equal to 1 and not the minimum value of 0. If a sum of the rise time and the fall time corresponding to transitioning between the gray-scale values 0 and 255 is 5 milliseconds (ms) and the sum of the rise time and the fall time corresponding to transitioning between the gray-scale values 1 and 253 is several tens of milliseconds, the response time is lengthened.
To achieve a full-color display, a display device applies red, green and blue filters. If the display device misjudges the level of the signals corresponding to the different colors, brightness differences may occur when the red, green and blue colors are outputted, which can cause the longitudinal ripple (mura) phenomenon.